On to the final lap [87.0 hours]

With the bulk of the Avionics, wiring and software work done, I’ve spent the past few months back on airframe and related work, pushing towards the point where I’m ready to take everything to the hangar. Lots of small to medium scale jobs, chipping away at the overall task. Here’s what I’ve done:

  • Wing wiring. I ran and labelled all wiring for both wings, and temporarily hooked up with wingtips, pitot, etc. and all connections to the fuselage, with the wings still sitting in the wing stand. I tested all functions, and found two minor issues – the landing and wigwag switches were reversed, and I had forgotten to run a wire from right to left side for the strobe synchronization. Apart from this, all good so I could now close up the wings.
  • Riveted bottom wing skins. This was a tedious job, which we did with each wing in turn laid flat on a pair of workbenches. The first wing took about 12 sessions across 4 days. Then we had a break for about a week, before tackling the second wing which took about the same number of sessions but stretched across a few extra days. Not many pictures of this, didn’t do much that deviated from the instructions, but due to the size of my forearms I found it impossible to reach down to the rear spar between the close-together ribs under the wing walk doubler. I made up a special long bucking bar, by taping a tungsten bar on the end of the RV-10 elevator bucking bar, which I could then hold in position. Not a great option, but good enough to get the job done cleanly.
  • Clear coat and install the centre console. This went in OK, as did the headset panels I previously designed and made up. Also included in this area are the throttle and pitch controls, fuel valve extensions etc. It’ll be a mild nuisance to take apart at each annual, but with the tunnel cover breaks I have in place won’t be too bad. The finished look is great.
  • Fitted the Matco brakes, brake lines, and filled the system with brake fluid. I replaced the standard O-rings in the Matco brakes with Viton rings, for high temperature stability, since I never need to worry about deep sub-zero conditions in Australia. I used Royco 782 brake fluid. No leaks, thankfully.
  • Wheel spats. Another tedious activity. I mostly followed the plans, except:
    • I used the RVbits leg intersection fairings, because the ones supplied in the kit are terrible.
    • I used a laser level for all the relevant measurements, much easier than plumb bobs etc.
    • I found my jacks crept down a bit over time, which is a problem for doing the spats because it takes a succession of fiberglass jobs over several days to do it all. I made up a wooden stand, that went under the main spar (with 3/16″ of hard rubber padding), used the jacks to raise it all, then lowered the stand onto wooden boards. A few Alclad shims under one side was enough to level the airframe in roll, and a tie-down on the tail was used to get the pitch into the cruise attitude. When it came time to do the nose wheel, I raised it higher by adding an extra board under each side and re-leveling.
    • I split the lower main wheel leg intersection fairings on each side, and fiber glassed the fairings into the respective front and rear spat halves. This is a bit more work to get right, but makes it simpler and easier to remove and reinstall the spats.
    • I painted the inside of the spats. I figure they’ll fill up with dirt and mud and require cleanout occasionally, and this seals up the fiberglass interior to make it easier to wash any accumulations away.
    • Since I’m using the Matco brakes, I had to cut out a section of the main wheel fairing brackets, to clear the brake line connection. I reinforced the area with some scrap Alclad to restore stability to this part.
    • The gaps between the front and rear spat halves, particularly on the nose gear fairings, were a bit irregular so I took the time to fix them up with micro.
  • Finalized everything behind the baggage bulkhead so that I can rivet on the final top skin.
  • All sorts of miscellaneous jobs, too numerous to list. These seem to be never-ending.

I’ve come to realize that if I don’t move everything to the hangar soon, it may become too wet and muddy around the workshop over the winter months to easily do the move. The mud around here is amazing – it can be like grease without too much rain at all. My current activities are aimed around doing this move in the coming weeks.

  • aaa_bottom_skins
    Riveting bottom wing skins
  • f61c
    Improvised bucking bar for rear spar rivets under wing walk area
  • aaa_wing_skins
    Inevitable side effect of riveting bottom wing skins
  • f61d
    Aligning the main leg fairings
  • f61e
    Work on the "split" bottom leg fairings
  • f61f
    Working on nose wheel fairing
  • f61m
    Fairing support bracket modified for Matco brakes
  • f61l
    Fairing support bracket modified for Matco brakes
  • f61k
    Right main fairings
  • f61i
    Left main wheel fairings
  • f61h
    Split leg fairing, left side
  • f61g
    Split leg fairing, right side
  • f61j
    Nose wheel, leg fairings
  • aaa_painting_spats
    Painting insides of spats etc.
  • f61a
    Centre console fitted
  • g1i
    Overhead panels in place

Where did winter 2020 go? [100.0 hours]

I got an E-mail from someone wondering why I stopped posting.

I’ve been steadily working the project, but having reached the “90% done, 90% to go” stage, it’s been hard to progress many tasks through to completion. Winter down in Tassie was long and cold as usual, and the short days tend to slow down workshop hours. Thankfully that’s now behind me for the year.

The inlet plenum 3D printing work reached a stalemate. After many Covid delays, I received the second prototype and it was damaged in transit due to poor packing. I worked with the vendor and insurance to have it replaced, and after yet more Covid delays the replacement arrived, also smashed in shipment. I was able to tape together enough pieces from the two parts to decide that the shape was going to be correct; however, I lost faith in the high temperature epoxy material – it was clearly too brittle. The correct material is ASA, but the quality of the first prototype was not good enough. In order to compete in online 3D printing services you need the lowest price, and there’s a big difference between how this first prototype was printed and how I would want it done. I talked to a few vendors in Australia, and it was clear that the cost would rapidly escalate into the thousands of dollars, for each printing, and I might want to do more adjustments yet. I decided to shelve the work, and ordered a commercial grade large form 3D printer. After months of delays, some again due to Covid-19, this thing will arrive here next week. The only problem is it arrives in 8 boxes and I have to assemble it. Once I get it up and running, I’ll be able to print the plenum as many times as I care to, with the quality I want, before calling it right.

I designed all the overhead panels, some auxiliary panels for headset connections etc, and settled on the replacement lower panel arrangement for the Aerosport 310, which was previously incorrect. I worked with AFS to get these designs finalized and the panels are being cut and printed at this time. In the meantime, I made some cardboard replicas and used these to do most of the overhead wiring. I’m not willing to post a photo of that.

I’ve been doing the wiring, which is a big job for an RV-10 made bigger by my choice of 2 batteries, 2 alternators, a 3 screen panel, A/C and SDS EFI. The wiring is about half done overall, and currently looks like a disaster. I started out wanting to simply do the wiring behind the baggage bulkhead and through the overhead, so that I could finish up the tail and put the final skin on. This plan rapidly devolved into an acceptance that I had to do all of the wiring, there are too many interactions to lock up one part before all parts of the puzzle are solved.

Associated with the wiring are some custom electronics. These pieces are:

  • Backup EFIS power. The backup EFIS power nominally comes from the second battery/alternator supply. However, what is the action in the case of an electrical fire and smoke starting to fill the cabin? It has to be “both masters off”, there’s no time to figure out which system is the problem. The engine will keep running because the EFI system is separately powered, but in order to keep minimal EFIS functionality, the regular backup battery must be used. So, I designed a board which will supply backup power to the AFS system, which will come from the secondary battery/alternator system if it is running, otherwise will come from a backup battery. Changeover is automatic, and the functions are ground tested as part of the runups.
  • SDS EFI power. Although the ignition systems, the two fuel pumps and the two ECU’s are on physically redundant battery+alternator systems, there is only one set of injectors so I needed what some would call an “essential bus” to run the fuel injectors. Any place physically redundant systems have to come together is a problem so I’ve applied some effort to this which I’ll post more about in a few months time.
  • Monitoring and logging. Between the extra TFT display on the panel, the EFI power system, the battery backup system and the A/C there are various sensors and data monitoring that I wanted brought back to a central non-essential point. A small embedded computer system sits under the pilot’s seat and has various communication methods to collect data and present information on the extra TFT display. This may eventually be a last resort backup EFIS, but not initially. I needed a set of interfaces for this embedded system that went beyond what is commercially available, so I’ve done a board for that as well. The prototype worked OK with a couple of jumpers and I’m re-spinning the board now.

In between all these activities, I found I was missing various miscellaneous/low-cost parts, which I’ve procured on a slow track with a few consolidated shipments from the US, again affected somewhat by Covid delays.

Reading through all of the above, it’s clear that I’ve done quite a bit over the past few months, but haven’t managed to actually finish anything. When I finally do manage to finish something, I’ll put up a celebratory post that will include some photos.

I have no idea how many hours I’ve spent on the above over winter – quite a lot – but I’m just going to log 100 hours because I really haven’t kept track of it all.

A/C Evaporator

I bought my A/C kit quite a few years ago from Airflow-Systems. I was shipped a so-called “Australian” evaporator, which is actually a product called a Monster Trunk System, part #685000-VUY from https://www.vintageair.com. There was a collection of metal parts and adapters in the kit, with no obvious way to set up the air flow and no instructions for this evaporator unit. The evaporator contains a 3 speed high volume scroll blower, which is ill suited to pressurizing the overhead console. Several other builders have supplemented this evaporator with an inline blower  which is more capable of pressurizing the overhead console. Yet another technique has been to forget about the overhead, turn the unit around and fit enough ducting to blow air straight into the cabin – see here.

I was already committed to a conventional mounting position, having done the inlet ducts and cutout for the overhead several years ago. What I needed to do was complete the evaporator outlet ducting, including an inline blower to suitably pressurize the overhead console, cabin flood air ducting, and a means to use the rear NACA vent air, via the Aerosport products NACA vent valve. This exercise is complicated by the fact that there isn’t a single right angle anywhere in the system, and it all rapidly turned into a 3D modelling exercise. First though, here’s a description of the evaporator inlet system I put together a few years ago:

The F-1006 bulkhead attachment for air to pressurize the overhead is a difficult area. In order to get enough air volume, a significant cutout is required. This mandates a doubler plate, and there is not much room to fit one. Edge distances, strength, clearances, Aerosport overhead console flange dimensions and screw positions for the rear baggage bulkhead all come into play. I wound up using both a shim plate and a doubler, in order to tie the doubler in with the rivets which secure the top of the F-1028 baggage bulkhead channel. Rivets for the doubler are flush on the rear side (where the manufactured heads are inside the overhead console air space) and flush on the front side where the baggage bulkhead overlaps the F-1006 flanges. I lowered and moved the normal position of the baggage bulkhead top screws, in theory they should have landed right in the middle of the Aerosport overhead lower flanges, in practice they are a little above this point but still easy enough to install.

This whole area is so busy, it is difficult to find a good way to “attach” the required air duct(s) to the bulkhead. It’s also not reasonable to have hard attachment points between the bulkhead and the evaporator/shelf, due to vibration and cracking. The idea of this design is to use a 3D printed bulkhead attachment block to achieve the following:

  • It can be fitted to the F-1006 bulkhead after the top skin is riveted on, sealed with some form of gasket material, and brings the air duct attachment plane clear of the bulkhead.
  • Two long #6 screws act as locating pins for the flange of the main attach duct.
  • A thick/soft gasket or manifold can be used between the rear of this bulkhead attachment point and the main duct, to seal airflow and provide vibration isolation.
  • If (when) the evaporator arrangement changes, a new 3D duct can be printed to mate with the existing bulkhead attachment point.

I use only one hole for airflow into the overhead, the side with more area (the F-1028 is offset from the center). Manifolding air into both sides complicates things and is pointless – what matters for overhead air is pressure, not volume. I wanted electrical connections into the overhead as well, so these are on the right hand side of the bulkhead, and will be sealed off in the overhead.

  • f20a
    Cutout for overhead air feed, with shim and doubler plates
  • f20b
    Holes for electrical conduits into overhead, with doubler plate
  • f20c
    3D printed template for bulkhead attach block, to verify it clears all obstacles.
  • f20d
    3D printed ABS bulkhead attach block, bulkhead side.
  • f20e
    Bulkhead attach block trial fit. Installation can only happen after top skin riveted on.
  • f20f
    A/C evaporator on shelf, with 3D printed inlets.
  • f20g
    3D printed inlets are contoured to match the curved front surfaces of the evaporator.
  • f54a
    Production inlet parts, made from tough epoxy, to replace the ABS prototypes
  • f54b
    Production inlet parts in place
  • f54c
    Cutouts done, nutplates in place
  • f54d
    I added a stiffener to the front face
  • f54e
    Fitting a rubber seal over the original evaporator inlet
  • f54f
    Cover plate in place, screwed on. Rubber pads on front of inlets, riveted on and sealant applied
  • f54g
    Cutout in evaporator shelf for receiver/dryer
  • f54h
    Clamping shroud for receiver/dryer

For the evaporator outlet, I designed a manifold which caters for the following requirements:

  • Fits onto the two irregular shaped outlets on the evaporator, with a simple rubber seal and some screws.
  • Provides an outlet for the inline blower. I used a 4″ blower, because it fits. A 3″ blower would probably also be adequate.
  • Provides a pair of outlets for cabin flood air. These should probably be 2.5 inches each, I used 2 inches because that’s the attachment size I have room for on the front (top) bulkhead.
  • Provides a pair of inlets for the Aerosport NACA vent valve, to feed vent air from outside into the system
  • Provides a place to mount a temperature probe
  • Can be assembled in-place, or if necessary by lowering the rear edge of the evaporator shelf (after removing the support).

The following pictures show what I came up with. I had the prototype fabricated in tough epoxy, and it fitted fine except for an indentation on the top that I made to clear the top stiffener. For some reason my measurements were off, and the indentation missed the stiffener by 20mm. I fixed this up and made some other improvements, and just ordered the final version which should arrive here in another week or so.

The 4″ blower just fits in the required space. I’m mounting it to a metal bracket that will be riveted to the cover plate I made up for the evaporator inlet. Also mounted on this cover plate are three relays (for the scroll fan) and a pwm controller for the inline blower. A wiring harness for this can be seen in the pictures, not properly laced up or secured yet. A high side pressure sensor, and evaporator air outlet temperature sensor, are included. The system controls will be on the overhead, except for the master “A/C on” switch which is on the front panel, pilot’s side. Turning the A/C off (before rolling) will be on the pre takeoff checklist, if necessary it can be re-engaged at some point during climb out. Part of the wiring includes a connector that could be used for a micro-controller that would be capable of climate control, if the rotary switch in the overhead is set to the “auto” position.

The final duct is to go from the outlet of the axial blower to the overhead. I printed some prototypes for this on my own consumer grade 3D printer using a flexible material. Once the shape was correct, I decided to order the production part in SLS Nylon. This will be very strong, but will still have enough flex to effectively detach the evaporator/blower assembly from the airframe. Although I will be assembling all of the final components with the top skin still partly open, everything is designed to be removable and reassemble-able after the skin is in place. It won’t necessarily be pleasant working back there in the hell hole, but it can be done. For assembly, I’m going to take advantage of the skin being off and will cheat as follows:

  • With everything in the tailcone finished, and with the evaporator/shelf removed, cleco the top skin on in its entirety. With Rosie outside on the rivet gun, and me inside, we’ll rivet the holes across the front and towards the rear on each of the three stiffeners.
  • Remove all the remaining clecos, allowing access from each side.
  • Fit the bulkhead adapter and the (flexible) duct from the inline blower outlet to the bulkhead. This can’t be done until after the (above) rivets are set.
  • Install the evaporator, shelf, outlet manifold, inline blower, NACA vent valve etc, using the access from each side to make the job easier this first time.
  • Fit the remaining refrigerant hoses etc. and charge the system. I plan to use an electric motor with a grooved pulley and a long serpentine belt as a means to run the compressor for this step.
  • Check for leaks and proper operation.
  • Cleco the skin back up, climb inside and finish riveting on the skin.
  • evap_out-1
    Evaporator outlet manifold
  • evap_out-2
    Top view
  • evap_out-3
    Bottom view
  • evap_out-4
    Right side view
  • evap_out-5
    Left side view, small hole is for temperature sensor
  • evap_out-6
    Front pump, vent attachments
  • evap_out-7
    Rear vent attachments, slot for top stiffener
  • evap_out-8
    Evaporator and vent attachment points
  • f56a
    Back from the printer
  • f56e
    Left side, temperature sensor
  • f56f
    Temperature sensor
  • f56g
    Aerosport NACA vent valve in place
  • f56h
    Left side cabin vent scat tube attachment point
  • f56i
    Right side clearances OK
  • f56j
    Top view
  • f56k
    There's just one problem....
  • f56b
    Bulkhead adapter 3D printed in tough epoxy
  • f56c
    Bulk attachment point
  • f56d
    Bulkhead adapter in place
  • ba2
    Bulkhead adapter design
  • ba1
    Bulkhead adapter, left side view
  • ba3
    Bulkhead adapter design
  • f56l
    Printing the bulkhead adapter prototype
  • f56m
    Finished bulkhead adaptor prototype
  • f56n
    TPU is very flexible
  • f56o
    Top view with bulkhead adaptor prototype in place
  • f56p
    Checking bulkhead adaptor prototype fit
  • f56q
    Side view of bulkhead adaptor prototype